1. Technical Field
The present invention relates to a light-emitting device including a light-emitting element and to an electronic apparatus including the light-emitting device.
2. Related Art
Top emission light-emitting devices are often used as display devices or the like of electronic apparatuses. A top emission light-emitting device is a type of light-emitting device from which light emitted from an organic electroluminescent (EL) element on a substrate is extracted to a direction opposite to the substrate. A typical top emission structure includes a light-emitting element between two electrodes, and a reflection layer disposed between a substrate and one of the two electrodes, first electrode (for example, anode), closer to the substrate so that light is extracted through the other electrode or second electrode (for example, cathode). In such a top emission light-emitting device, light is efficiently used.
A technique (for example, SID2010 P-146, S. Lee, Samsung Mobile Display Co., Ltd.) is disclosed of increasing the light extraction efficiency of such a top emission light-emitting device by using a white light-emitting element and allowing light having predetermined wavelengths to resonate between the second electrode and the reflection layer. For this resonant structure, an optical structure satisfying the following equation has been proposed:D={(2πm+φL+φU)/4π}λ  (1)
where λ represents the peak wavelength of the resonant structure, D represents the optical length from the reflection layer to the second electrode, φL represents the phase sift of reflection from the first electrode, φU represents the phase shift of reflection from the second electrode, and m represents an integer.
In particular, in the case of m=0, light having a wide range of wavelengths can be extracted with a certain level of efficiency, while the array of organic EL elements is simplified. Accordingly, the cost of the light-emitting device can be reduced, and high-definition pixels can be easily formed.
However, when m is 0, the light-emitting device having an optical structure satisfying equation (1) allows the extraction of light having wavelengths in the all regions of red, green and blue. Accordingly, colors for the red, green and blue pixels are separated through color filters or the like. This causes the band of the emission spectrum to broaden and is accordingly liable to reduce color purity. Also, light extraction efficiency tends to be reduced for each color of the red, green and blue regions. Consequently, the power consumption of the light-emitting device is increased. This is disadvantageous in terms of panel properties.
In order to increase color purity and light extraction efficiency, for example, Japanese Patent No. 2797883 discloses a technique for controlling the optical length D of each of the red, green and blue pixels. Unfortunately, since the optical length D is controlled for each pixel, the technique of the cited patent document results in a complicated pixel structure and increases the number of process steps. In addition, the process for forming high-definition pixels using the technique of this patent document is liable to be limited by the line width of the circuit pattern and results in a reduced aperture ratio. Furthermore, the light-emitting device produced using this technique has a large variation in the thicknesses of the layers from the reflection layer to the semitransmissive reflection layer and accordingly exhibits large changes in chromaticity.
Accordingly, in order to achieve a simple pixel structure capable of reducing the manufacturing cost, to facilitate the production of high-definition small pixels, and to suppress chromaticity changes resulting from the variation in thickness, organic EL elements having an optical structure satisfying equation (1) with m=0 are desired.
The use of color filters having sharp cut-off properties can be a solution for preventing the degradation of color purity in the production of such organic EL elements. In order to achieve sharp cut-off properties, the thickness of color filters is increased. However, in the manufacturing process of a high-definition small display panel, in which fine patters are difficult to from, color filters having sharp cut-off properties are also difficult to form. It is particularly difficult to form such color filters on a sealing layer. Also, materials that can form thick color filters are limited.